Devices for measuring cardiovascular properties suffer from the problem that the measurement itself interferes strongly with the state of the subject, thereby leading to erroneous results. This is especially the case for current cuff-based methods that may impart a significant physiological impact. In current cuff-based methods, the systolic blood pressure is obtained by completely or at least substantially blocking an artery, which in most cases is the brachial artery in the upper arm. Blocking the artery affects pulse pressure propagation and pulse pressure shapes, which may only be tolerated in the peripheral system. Further, the diastolic pressure is derived from measurements obtained when the transmural pressure (pressure difference between the outside and the inside of an artery) is close to zero, which implies those measurements are made under conditions that are far from normal.
It is also well recognized that traditional methods based on inflatable cuffs and measurements performed in a clinical environment may have strong psychological effects causing elevation of blood pressure. The phenomenon is commonly called “white coat syndrome” or “white coat hypertension.” So-called “masked hypertension” is a contrasting phenomenon in which blood pressure is elevated during normal daily activities but not in a medical office setting.
Additionally, blood pressure often exhibits considerable variability over time. Thus, identifying diurnal or other temporary variations in blood pressure may be very important for proper diagnosis of hypertension. It has also recently been shown that performing ambulatory blood pressure measurements is overall cost-effective.
It is therefore desirable to provide a device for measuring blood pressure that does not interfere with the normal bodily functions or at least does not perturb an artery being measured and that may measure blood pressure continuously and over a longer period of time.